Refining soybean oil



United States Patent O 3,093,667 REFINING SYBEAN GIL Richard J. Fiala, Decatur, Ill., assigner to A.. E. Staley Manufacturing Company, Decatur, Ill., a corporation of Delaware Filed Apr. 27, 1961, Ser. No. 106,103 11 Claims. (Cl. 260424) This invention relates, generally, to improvements and innovations in the processing or refining of soybean oil. More particularly, it pertains to innovations and improvements in the washing of soybean oil that has been degummed by the acid anhydride-water degumming treatment disclosed in Patent No. 2,782,216.

Prior to the commercial use of acetic anhydride in the degumming of soybean oil as taught in Patent No. 2,782,- 216, crude soybean oil had been treated according to the so-called alkali refining process for the dual purpose of degumming and neutralizing to obtain so-called break free, neutral soybean oil. Essentially, the alkali refining process consists of treating either crude soybean oil, or soybean oil which has been degummed with plain water, with aqueous caustic solution. The by-product of the alkali refining operation is known as soap stock and is a dark, greasy substance consisting mainly of a mixture of soaps, phosphatides, neutral oil and Water. If crude (undegummed) oil is alkali rened the soap stock includes all the phosphatides, and all of the free fatty acids as soap. When oil degummed with plain water is alkali refined, the soap stock will contain approximately of the phosphatides and from about one-half to two-thirds of the free fatty acids as soaps.

The main objection or drawback to the alkali refining technique is the unavoidable loss of valuable neutral oil, partly by entrainment or emulsification of neutral oil in the soap stock and partly by hydrolysis of the neutral oil. As the name implies, soap ystock has very little value and is sold as a low priced, low grade, by-product. 'I'he socalled acid anhydride degumming process disclosed in Patent No. 2,782,216 was a substantial improvement over the alkali refining process, particularly as applied to soybean oil, for several reasons, the more important being: it permitted break-free soybean oil to be obtained in the degumming operation alone without an additional alkali refining step; fatty `acids could be recovered in a single step as once-distilled fatty acids during the deodorization operation; the loss of neutral oil was substantially reduced; and, the deodorized break-free oil had excellent flavor and good stability.

The free fatty acid content of soybean oil degummed according to United States Patent 2,782,216 ranges from about 0.25 to about 1.5 percent by Weight of the oil calculated as oleic acid. Included in this content is residual lower fatty acid, e.g. acetic acid, derived from the degumming anhydride. One thousand pounds of the oil may contain from about 0.009 to about 0.053 pound equivalents of free fatty acid. The amount of sodium hydroxide required to neutralize the acid ranges from 0.36-2.l2 pounds.

Subsequent to the discovery of the acid anhydride degumming process as disclosed in Patent No. 2,782,216, it was discovered that the washing of the thus degummed oil could be improved in the following respects by incorporating in the wash Water small quantities of either certain phosphatic washing agents or of tannic acid as disclosed in Patents Nos. 2,881,195 and 2,792,411, respectively: Better separation of the water and oil phases was obtained; the oil losses in washing were decreased; and, the Washed degummed oils had improved color stability on heating.

It has now been found in accordance with the present invention that a number of unexpected improvements and 3,093,667 Patented June ll, 1963 advantages are obtainable by using small amounts of caustic soda or other alkali metal hydroxide in the washing of soybean oil that has been degummed with the use of an acid anhydride, e.g. acetic anhydride, as a degumming aid, such caustic soda or other alkali metal hydroxide being used in lieu of tanm'c acid or one of the phosphatic materials as disclosed in the above mentioned Patents 2,792,411 and 2,881,195, respectively.

One of the principal advantages accruing from the use of a small amount of caustic soda or other alkali metal hydroxide in the washing of soybean oil that has been degummed with acetic anhydride as a degumming aid, occurs in connection with certain crude soybean oils that are unusually difficult to degum by the acid anhydride degumming process. When these difficult-to-degum soybean oils were processed by the commercial acetic anhydride degumming process, either with or without a washing aid such as a phosphatic compound (eg. Calgon) or tannic acid, it was found that relatively high levels of phosphorus (i.e. over 50 parts per million of phosphorus) were left in the degummed oil. These residual phosphorus compounds led to a considerable amount of emulsification of neutral oil, free fatty acid, and wash water in the water washing step. Such emulsification loss of neutral oil in the water Wash step increased the wash loss of neutral oil from an average of 0.25% to the 0.5 to 3% range, thus substantially eliminating the improved yields normally obtainable with the acid anhydride degumming process.

It was unexpectedly discovered in accordance with the present invention that these wash step emulsions could be either completely or substantially eliminated by adding small amounts of caustic soda, or other alkali metal hydroxide, to the acid anhydride degummed soybean oil in the Washing step prior to separation of the wash water from the oil. It would normally have been expected and postulated that the use of alkali in -the washing of such difiicult-to-degum oils would have been of no avail and probably would make matters worse. Thus, it would normally be anticipated that the alkali would react with free fatty acids present to form soaps and that the soaps would tend to emulsify lthe oil and water, thereby increasing the emulsification loss of neutral oil. However, contrary to such expectations, the added sodium hydroxide does not act in this manner.

Representative data on neutral oil loss due to emulsification will further bring out the significance of the present invention. When normal or easily degummed soybean oils are treated according to the acetic anhydride degumming process and washed with a phosphatic material or tannic acid, the average or normal loss of neutral oil will be about 0.25%. However, when the same degumming process and washing techniques are applied to a difiicu-lt-to-degum oil then the loss of neutral oil in the wash water steeply rises to the range of 0.5-3%. Hence, the yield benefits attributed to the acetic anhydride degumming process disappear in the processing of these difficult-to-degum oils. However, by using a small amount of caustic soda or other alkali metal hydroxide in the Washing operation the losses of neutral oil in the wash water can be kept below 0.75% and within the range of 0.3% to 0.75 %-a loss of 0.45% to 0.60% being typical ,when the free fatty acid of the crude soybean oil is in the range 0.4-0.7%.

When the caustic soda is used in place of either a phosphatic material (eg. Calgon) or tannic acid in the wash water treatment of a normal or easily degummed soybean oil that has been treated with acetic anhydride, then the loss in the washing step is somewhat greater than it would be with one of the phosphatic materials or tannic acid. For example, in such a case, the wash loss with caustic soda will run from 0.3% to 0.75%,

3 whereas, on the average using either Calgon or tannic acid in the wash water, the loss will be around 0.25%. The primary reasons for this difference is the removal of free fatty acid (FFA) in the caustic wash step, the loss of neutral oil not `being appreciably different. Even though such use of caustic soda results in higher washing losses of free fatty acids in the washing of acetic anhydride degummed soybean oils that were easily degummed or responded normally to such treatment, it `was found that certain other advantages resulted from the use of caustic soda in place of a phosphatic material or tannic acid. For example, there is a substantial reduction in costs due to reduced bleach losses, reduced requirements of Ibleaching earth, and reduced cost of acetic anhydride. Furthermore, from the standpoint of quality, by reason of using the caustic soda in place of the phosphatic material or tannic acid in the wash water, the iron content of the oil is significantly reduced, the Lovibond color and the bleachability are improved, the chlorophyll con- 'tent is reduced and lthe free fatty acid content is lower.

It should also be mentioned that with diiiicult-to-degum soybean oils, the increased loss of neutral oil experienced in employing the commercial acetic anhydride degumming process was only one difficulty that was noted. In addition it was found that the bleaching earth requirements were greatly increased, and Vthere was an increased tendency toward color reversion. Each of lthese problems, as well as the increase in loss of neutral oil, was eliminated or substantially overcome by the use of caustic wash step following the degumming with acetic anhydride.

Accordingly, while the present invention has special utility in connection with the degumming of soybean oils that are `diiicult to degum with acetic anhydride, the invention also has utility and advantages in connection with the washing of Anormal or easily degummed soybean oil, as explained above.

The object of this invention, generally stated, is the improvement in washing soybean oil degummed with the use of acid anhydride which resides in incorporating a small amount of caustic soda or fthe like during the washing -of the degumnied oil thereby substantially lowering the loss of neutral oil due to emulsiiication.

A further `object of the present invention is the use of caustic soda or `other alkali metal hydroxide in a small amount in the washing of soybean oil that has been degummed with the use of acetic anhydride so as to reduce the iron content of the degummed oil, improve the Lovibond color and bleachability, reduce the chlorophyll and free fatty acid contents, and reduce the use of bleaching earth and acetic anhydride required.

Certain other objects of the invention will, in part, be obvious and will in part appear hereinafter.

-For a more complete understanding of the nature and scope of the invention reference may now be had to the following detailed description-thereof wherein an illustrative example is set forth in connection with the ow sheet contained in the accompanying drawing.

One general embodiment or precedure for practicing r,the invention will be described in connection with the accompanying drawing, following which a specic working example will be given.

Referring to the drawing, crude soybean oil is fed through line 6 containing a heat exchanger S for adjusting the temperature of the crude oil to that which is established for best treating conditions before it is deliveredinto the hydrating tank 9 equipped with a power stirrer. Acetic anhydride (or other selected acid anhydride) is delivered into line 6 through a line It?` from a suitable supply. Water is introduced as needed into the tank 9 through water line 11. The oil-water mix is retained in the hydration tank 9 where a minimum 15- minute contact period is established. The oil-water mixture in this tank is agitated to prevent the hydrated gums from falling out. The oil-water mixture is then fed through line 12 to the suction side of a centrifugal pump 7. The discharge connection y of the pump 7 communicates through a line 14 to the feed or inlet connection of a known type continuous centrifugal separator designated at 15. There are several well known centrifugal separators available in this country that may be used, e..g. the Podbielniak, De Laval and Westphalia continuous separators or centrifuges. An automatic flow controller 16 of known type is provided in line 14 for regulating the iiow rate into the separator 15 at a predetermined value.

In the continuous centrifuge ,15 the aqueous phase is separated from the degummed oil and discharged through line 17 ias so-called wet gums, while degummed oil discharges through line 18 into a stirrer-equipped, degumrned oil tank 2t?. The lines 17 and 18 are provided with pressure regulators 1 9 of known type which automatically control the operation of the separator 15 in conjunction with the automatic ow controller 16. The degummed oil tank 20 is connected with a discharge line 21 which communicates with a second centrifugal pump 26. The line 21 is provided with a heat exchanger 23 and lines 24 and 25 for supplying water and caustic soda solution, respectively, to the line 21. The discharge connection 27 of the pump 26 is connected by way of line 28 containing an automatic flow controller 29 to the inlet connection of a second continuous centrifugal separator indicated at 35i. `Inthe centrifuge 30 the degummed oil washed with caustic soda solution is separated into oil and aqueous phases, with the waste wash water being discharged from the centrifuge through line 32. while the alkali washed oil is discharged through line 33 into an alkali washed oil receiving tank 35. Lines 32 and 33 are equipped with automatic pressure regulators 31 which automatically control the operat-ion of the separator 30 in conjunction with the ow controller 29.

The caustic washed oil is drawn from the tank 34 through the line 35 into the inlet connection of a pump 36 with fresh wash water being added through line 37. The pump 36 discharges the oil and water mixture through line 38 equipped with automatic iiow controller 39 into a third continuous centrifuge 40. The wash water from the centrifuge 40 is discharged through line 42 while the washed oil is discharged through line 43 to a storage tank 44. Lines 42 and 43 are both provided with automatic pressure controllers 41.

As indicated in the drawing, the ow lines 6, 10, 11, 24, 25 and 37 are provided with suitable valves in order that ow therethrough may be regulated or entirely closed olf, as desired.

The following example will serve to disclose one specific procedure by which the present invention may be practiced utilizing the equipment described above in connection with the drawing.

Example 1 Crude soybean oil that was found to be difficult-todegum by the commercial version of the acid anhydride process described in Patents 2,792,411 and 2,881,195 is introduced into line 6 at the rate of 72 gallons per minute. On passing through the heater 8 the temperature of the crude oil is raised to about F. Acetic anhydride is introduced from line 10 into the stream of crude oil Kat the rate of 0.65 lb. per minute which equals 0.12% by weight of the crude oil tiow. Water is added to the stream of crude oil from pipe 12 at the rate of 1.3-1.9 gallons per minute which equals 2-3% by weight of the crude oil. rIhe pump 7 is operated to give a discharge pressure of approximately 140 pounds per square inch gauge.

The centrifugal separator 15 operates to continuously form and discharge a stream of wet gums through the discharge line 17 and another stream of the degummed oil through line 18 which is delivered into the tank 20 from which it is being continually withdrawn through repeated, omitting the -addition of sodium hydroxide to the wash water. The nal washed oil is break free.

In the light of the foregoing disclosure those skilled in the art will be able to practice the invention either according to the specific embodiments and directions set forth above, or according to other embodiments which will be obvious. Accordingly, the foregoing disclosure is intended to be interpreted as illustrated and not in a limiting sense.

What is claimed as new is:

1. In the processing of soybean oil wherein the crude oil is first degummed with water containing a small amount of at least one acid anhydride selected from the group consisting of lower alkyl aliphatic monobasic and dibasic aci-d anhydrides as a degumming aid, next the wet gums `are separated from the oil, and then the degummed oil is washed, the improvement in the washing operation which comprises, washing the degummed oil without any intervening treatment and in a non-attenuated condition with from -about 50% to 200% by weight of the alkali metal hydroxide required to neutralize the free fatty acid content of the degummed oil.

2. In the processing of soybean oil wherein the crude oil `is rst water degummed with water containing a small amount of acetic anhydride as a degumming aid, next the wet gums are separated from the oil, andthen the degurnmed oil is washed, the improvement in the washing operation which comprises, Washing the degumrned oil without any intervening treatment and in a non-attenuated condition in the presence of about 50% v-to 200% by Weight of the alkali metal hydroxide required to neutralize the free fatty acid content of the degummed oil.

3. In the processing of soybean oil wherein the crude oil is first Water degummed with water containing a small amount of acetic anhydride as a degumrning aid, next the wet gums are separated from the oil, and then the degummed oil is washed, the improvement in ythe washing operation which comprises, washing the degummed oil without any intervening treatment and in a non-attenuated condition in the presence of about 50% to 200% by weight of the sodium hydroxide required to neutralize the free fatty acid content of the degummed oil.

4. In the processing of soybean oil wherein the crude oil is rst water degummed with water containing a small :amount of acetic anhydride as `a degumming aid, next the wet gums are separated from the oil, and then the degummed oil is washed, the improvement in the washing operation which comprises, washing the degummed oil without any intervening treatment and in a non-attenuated condition in the presence of about to of the sodium hydroxide required to neutralize the free fatty `acid content `of the rdegummed oil.

5. The improvement of claim 3 wherein the degummed oil is -contacted with an aqueous solution containing from about 1% :to 3% by weight of alkali.

6. The improvement of claim 4 wherein the degummed oil is contacted with an aqueous solution containing from about 1% to 3% by weight of alkali.

7. The improvement of claim 3 wherein said Washing is conducted at a temperature in the range of about to 200 F.

8. The improvement of claim 3 wherein said washing is conducted at a temperature of at least about 180 F.

9. The improvement of claim 4 wherein said washing is conducted at a temperature in the range of about 160 to 200 F.

10. The improvement of claim 4 wherein said washing is conducted at a temperature of at least about 180 F.

11. The improvement of claim 3 wherein after said washing with `sodium hydroxide the aqueous phase is separated from the oil phase, and the resulting alkaliwashed oil is Washed at least once with plain water.

References Cited in the file of this patent UNITED STATES PATENTS 2,337,041 Giles et al Dec. 21, 1943 2,666,074 Sadler Jan. l2, 1954 2,782,216 Hayes Feb. 19, 1957 

4. IN THE PROCESSING OF SOYBEAN OIL WHEREIN THE CRUDE OIL IS FIRST WATER DEGUMMED WITH WATER CONTAINING A SMALL AMOUNT OF ACETIC ANHYDRIDE AS A DEGUMMING AID, NEXT THE WET GUMS ARE SEPARATED FROM THE OIL, AND THEN THE DEGUMMED OIL IS WASHED, THE IMPROVEMENT IN THE WASHING OPERATION WHICH COMPRISES, WASHING THE DEGUMMED OIL WITHOUT ANY INTERVENING TREATMENT AND IN A NON-ATTENUATED CONDITION IN THE PRESENCE OF ABOUT 125% TO 130% OF THE SODIUM HYDROXIDE REQUIRED TO NEUTRALLIZE THE FREE FATTY ACID CONTENT OF THE DEGUMMED OIL. 